Physicists solve mystery of why cats rule, dogs drool

Popular web videos showing that "cats rule and dogs drool" have new scientific evidence to support that felinophilic sentiment, at least when it comes to drinking.

While cats expertly manipulate water to quench thirst neatly, dogs smash, slosh, spill, and splash their way, according to research unveiled on Monday.

The latest findings, which focus on dogs and were presented at a meeting in San Francisco of the American Physical Society, build on an earlier discovery of how cats drink. Neither cats nor dogs can close their cheeks tightly enough to create suction, as humans do, so exactly how they manage had been a puzzle.

In 2010, engineers at Princeton University and the Massachusetts Institute of Technology, among other schools, discovered how cats lap water. Basically, felines touch their tongue to the water's surface without penetrating it, and pull up a column of liquid at a speed of 3 feet (1 meter) per second. Just before gravity pulls the water down, cats slam their mouth shut over the top of the column four times per second, swallow, and repeat.

When the dog study started, the scientists thought dogs would turn out to drink similarly to cats, said biomechanical engineer Sunny Jung of Virginia Tech, a member of the cat team who also led the dog research. Not so.

For one thing, cats' tongues gently touch the water surface, but dogs' smash through it, as cameras under a water trough showed. Dogs "make lots of splashing, but a cat never does," Jung said.

Also, cats pull up their tongue to create the water column with a force up to twice that of gravity. Dogs create a force up to eight times gravity.

Finally, although only the tip of a cat's tongue touches the water, a large area of the dog's does, making them sloppy drinkers. More precisely, the volume of water a dog's tongue can move increases exponentially with body size. Which is why Saint Bernards, but not dachshunds, turn kitchen floors into lakes.